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Single-Crystal Silicon Carbide MEMS: Fabrication, Characterization, and Reliability 7-17

the theoretical ideal I–V characteristic, depending on the integrity of the metal/epilayer interface. The
saturation current density, J , is expressed as:
s

qφ
B
2
J A*T e kT (7.15b)
s
2
2
where A* is the effective Richardson constant (Acm K ), and φ (V) is the Schottky Barrier Height
B
(SBH) between the metal in intimate contact with the 6H-SiC epilayer. The ideality factors before and
2
after annealing was ranged from 1 to 1.05 and J in the range of 9.44 10 8 to 4.4 10 3 (Acm ). In
s
this work, the effective Richardson constant was estimated by
2
2
A* 120(m*/m ) [Acm K ] (7.15c)
e
o
where m*/m is the ratio of the effective electron mass to the electronic rest mass. For a value of 0.45m ,
e o o
2
2
A* was calculated to be 54Acm K . The obtained average SBH values ranged from 0.54 to 0.84 eV. The
ohmic contact obtained after annealing is believed to be a result of the barrier-lowering effect caused by
the change at the metal/SiC interface during annealing.
The Auger Electron Spectroscopy (AES) depth profile of Figure 7.12(a) indicated distinct boundaries
of the as-deposited metals on the SiC epilayer. However, in Figure 7.12(b), intermixing and zone reactions
after annealing are evident, and a new layer consisting mainly of Pt, Ti, Si, and C atoms is observed in

100

Pt Ti Ti + N Si C O
80
At. conc. (%) 60

40

20

0
0 10 20 30
(a) Sputter time (min.)

100
Pt Ti Si C O
80
At. conc. (%) 60

40

20

0
0 10 20 30 40
(b) Sputter time (min.)

FIGURE 7.12 (a) Auger Electron Spectroscopy depth profile of as-deposited Ti/TiN/Pt metallization on n-type 6H-
SiC. (b) Auger Electron Spectroscopy of Ti/TiN/Pt after rapid thermal anneal at 1000°C for thirty seconds in argon
atmosphere. Synchronous 2:1 ratio tracking between titanium and carbon suggested the formation of TiC 1-x on the
epilayer surface.

© 2006 by Taylor & Francis Group, LLC